1. Field of the Invention
The present invention relates to a water-cooled vertical engine having a crankshaft disposed substantially vertically and being provided with a water jacket in each of a cylinder block, a cylinder head, and exhaust passage means. The present invention also relates to an outboard motor provided with the water-cooled vertical engine and, furthermore, the present invention relates to an outboard motor provided with an engine that is cooled by means of a cooling medium. Moreover, the present invention relates to a water-cooled vertical engine provided with an exhaust passage cooling water jacket, a cylinder block cooling water jacket, and a cylinder head cooling water jacket, and an outboard motor equipped therewith.
2. Description of the Related Art
As a vertical engine for an outboard motor, a water-cooled engine is generally used. In this type of water-cooled engine, when a cylinder block and a cylinder head are equally cooled with cooling water, if the cylinder head, which generates a comparatively large amount of heat, is cooled to an appropriate temperature, then the cylinder block, which generates a comparatively small amount of heat, tends to be overcooled. An outboard motor cooling structure that can solve such a problem and cools both the cylinder head and the cylinder block to appropriate temperatures is known from Japanese Patent Application Laid-open No. 61-167111.
In embodiments and modification thereof described in Japanese Patent Application Laid-open No. 61-167111 (see FIG. 2, FIG. 2a to FIG. 2c, FIG. 3, FIG. 3a and FIG. 3b), by supplying low temperature cooling water from a cooling water pump to a cylinder head water jacket and supplying the cooling water having a temperature increased thereby to a cylinder block water jacket, the cylinder block is prevented from being overcooled while the cylinder head is cooled sufficiently.
However, the above-mentioned conventional arrangement is unsatisfactory with respect to the following matters.
That is, a type (see FIG. 2 and FIG. 2a) in which the temperature of cooling water flowing in from an upper inlet of the cylinder head water jacket is controlled by means of a thermostat provided at a lower outlet of the cylinder head water jacket has the problem that when the thermostat closes when the temperature is low, such as while idling, the flow of cooling water within the cylinder head water jacket is held back, and the tracking ability of the thermostat becomes poor. Even when a switch-over valve for switching over cooling water passages is used, the thermostat cannot follow up rapid changes in running conditions, and it is difficult to control the temperature of the cooling water satisfactorily. Above all, since cooling water does not flow into the cylinder block water jacket until the thermostat opens, the engine is not suitable when running at very low temperature. Furthermore, in a type (see FIG. 2b) in which the temperature of cooling water that flows in from an upper inlet of the cylinder head water jacket is controlled by means of a thermostat provided at an upper outlet of the cylinder block water jacket, the distance from the inlet of the cylinder head water jacket to the thermostat is long, and the ability of the thermostat to follow up the cooling water temperature at the inlet of the cylinder head water jacket which is far way from the thermostat, is poor.
In a type (see FIG. 2c and FIG. 3a) in which the temperature of cooling water flowing in from a lower inlet of the cylinder head water jacket is controlled by means of a thermostat provided at an upper exit of the cylinder head water jacket, since the temperature of cooling water on the cylinder block side cannot be controlled directly, it is difficult to obtain an appropriate cooling effect. In a type (see FIG. 3) in which the temperature of cooling water flowing in from a lower inlet of the cylinder head water jacket is controlled by means of a thermostat provided at an upper exit of the cylinder head water jacket, and the temperature of cooling water flowing in from a lower inlet of the cylinder block water jacket is controlled by means of a thermostat provided at an upper exit of the cylinder head water jacket, there is the same problems as those of FIG. 2, FIG. 2a, FIG. 2c, and FIG. 3a described above, that is, cooling water is not supplied to the cylinder block water jacket until the thermostat on the cylinder head side opens, and this type also has the same defect as above with respect to a switch-over valve for switching over cooling water passages. Moreover, in a type (see FIG. 3b) in which the temperature of cooling water flowing in from a lower inlet of the cylinder head water jacket is controlled by means of a thermostat provided at an upper exit of the cylinder block water jacket, there is the same problem as that of FIG. 2b described above, that is, the distance from the inlet of the cylinder head water jacket to the thermostat is long.
Furthermore, when the cylinder block and the cylinder head of a water-cooled engine are cooled equally with cooling water, if the cylinder head, which generates a comparatively large amount of heat, is cooled to an appropriate temperature, then the cylinder block, which generates a comparatively small amount of heat, tends to be overcooled. Under these circumstances, an engine cooling system for cooling both the cylinder head and the cylinder block to appropriate temperatures is known from Japanese Patent Publication No. 2-3014.
In the system disclosed in Japanese Patent Publication No. 2-3014, a cylinder block cooling water jacket and a cylinder head cooling water jacket are provided independently, the cooling water temperature of each of the two water jackets is detected by means of a corresponding cooling water temperature sensor, and the amounts of cooling water distributed to the two water jackets are controlled based on the detected cooling water temperatures.
Moreover, a water-cooled vertical engine equipped with an exhaust passage cooling water jacket in addition to a cylinder block cooling water jacket and a cylinder head cooling water jacket requires a total of three cooling water temperature sensors if a cooling water temperature sensor is to be provided in each of the water jackets.